Ablation of myocardial tissue is well known as a treatment for cardiac arrhythmias. In radio-frequency (RF) ablation, for example a catheter is inserted into the heart and brought into contact with tissue at a target location. RF energy is then applied through an electrode on the catheter in order to create a lesion for the purpose of breaking current conduction paths in the tissue.
Additionally, the use of renal neurostimulation for the treatment of heart arrhythmias was disclosed in U.S. Patent Publication No. 2007/1029671 by Demaris et al. Demaris sets forth the use of neuromodulation to effectuate irreversible electroporation or electrofusion, ablation, necrosis and/or inducement of apoptosis, alteration of gene expression, action potential attenuation or blockade, changes in cytokine up-regulation and other conditions in target neural fibers. In some embodiments, such neuromodulation is achieved through application of neuromodulatory agents, thermal energy, or high intensity focused ultrasound.
In U.S. Patent Publication No. 2010/0222851 by Deem et al. the monitoring of renal neuromodulation was proposed stimulation to identify renal nerves to denervate or modulate. Stimulation of such nerves prior to neural modulation would be expected to reduce blood flow while stimulation after neural modulation would not be expected to reduce blood flow to the same degree when utilizing similar situation parameters and locations prior to neural modulation.
Recently, circumferential ablation of the pulmonary vein has gained acceptance as a treatment for atrial arrhythmias, and particularly for atrial fibrillation. For example, U.S. Pat. No. 6,064,902, whose disclosure is incorporated herein by reference, describes a catheter for ablating tissue on the inner wall of a blood vessel, such as a pulmonary vein. The tip portion of the catheter is deflectable from a first, generally straight, configuration, in which the proximal and distal sections are substantially co-linear, to a second, J-shaped, configuration in which the proximal and distal sections are generally parallel with a separation therebetween substantially corresponding to the inside diameter of the blood vessel. The distal end portion of the catheter is rotated about the longitudinal axis of the catheter to cause a circumferential displacement of proximal and distal ablation electrodes on the catheter along the inner wall of the pulmonary vein. In this way, the electrode catheter may be used to ablate a number of circumferentially-spaced sites on the inner wall of the pulmonary vein by ablating one or two sites at each circumferential position.
U.S. Patent Application Publication 2005/0033135, whose disclosure is incorporated herein by reference, describes a lasso for pulmonary vein mapping and ablation. A catheter for circumferentially mapping a pulmonary vein (PV) includes a curved section shaped to generally conform to the shape of the interior surface of the PV. The curved section is connected to catheter by a generally straight axial base section that is in an “on edge” configuration where the base axial section connects to the curved section on the circumference of the curved section. The curved section comprises one or more sensing electrodes, and its proximal end is joined at a fixed or generally known angle to a base section of the catheter. Position sensors are fixed to the curved section of the catheter and to the distal end of the base section. The catheter is inserted into the heart, and the curved section is positioned in contact with the wall of the PV, while the base section remains within the left atrium, typically positioned such that the joint with the curved section is at the ostium of the vein. The information generated by the three position sensors is used to calculate the locations and orientations of the sensing electrodes, which enables mapping of the surface of the PV. The sensing electrodes may additionally perform ablation of selected sites, or the catheter may further comprise ablation elements.
U.S. patent application Ser. No. 12/345,720, which is assigned to the assignee of the present patent application and whose disclosure is incorporated herein by reference, describes an alternative design in which the lasso is thicker and stiffer. Even so, operators can find lasso catheters to be difficult to maneuver within the heart and position in such a way that the entire circumference of the lasso is in contact with the tissue, as is desirable for effective pulmonary vein isolation.
U.S. patent application Ser. No. 13/174,742, which is assigned to the assignee of the present application and whose disclosure is incorporated herein by reference, describes a design which is adapted for use at the ostia or wall outside the vessel.
However, because human anatomy varies between individuals, the shape and size of a vessel such as a renal artery or a pulmonary vein vary, and the end section whether having an arcuate shape or a generally helical shape may not always fit the particular target ostium. Because of these factors, contact between the electrodes and the vessel wall is often less than complete and an ablation which effectively blocks conduction through the nerves in the vessel wall may not be complete. Accordingly, a desire exists for a catheter for ablation in a vessel which has a helical design so as to enable such an ablation in a vessel such as a renal artery or pulmonary vein.